This invention relates generally to the field of magnetic data storage devices, and more particularly, but not by way of limitation, to an actuator arm used to support a head adjacent a magnetic recording disc of a disc drive, the actuator arm incorporating a tapered trailing edge and a recessed surface to recess a head conductor used to provide electrical communication with the head.
Disc drives are used as primary data storage devices in modern computer systems and networks. A typical disc drive comprises a head-disc assembly (HDA) which houses mechanical portions of the drive, and a printed circuit board (PCB) mounted to an outer surface of the HDA which supports electronic circuitry used to control the HDA and facilitate communication between the disc drive an a host computer in which the drive is mounted.
A typical HDA includes one or more rigid magnetic storage discs which are journaled about a rotary hub of a spindle motor to form a rotatable disc pack. An actuator supports an array of heads adjacent tracks defined on the disc surfaces.
A typical actuator construction utilizes an actuator body configured to rotate about a stationary shaft adjacent the disc pack. A coil of a voice coil motor (VCM) projects from the body opposite the discs and is immersed in the magnetic field of a magnetic circuit. The application of current to the coil induces rotation of the body about the shaft.
A plurality of rigid actuator arms project from the body toward the discs with one arm above the topmost disc, one arm below the bottommost disc, and one arm between each adjacent pair of discs. Flexible suspension assemblies (xe2x80x9cflexuresxe2x80x9d) are supported at the distal ends of the actuator arms and in turn support the heads adjacent the disc recording surfaces. Thus, for a fully populated configuration where data are stored to each available disc recording surface, the top and bottom actuator arms are each configured to support one flexure/head combination, and each intermediary actuator arm supports two flexure/head combinations. Conductors are routed along the edges of the actuator arms and flexures to enable electrical communication between the heads and the disc drive control PCB.
The high-speed rotation of the discs induces air currents that generally flow parallel to and in the direction of rotation of the discs. The heads are configured with aerodynamic features that enable the heads to be supported in close proximity to the rotating disc surfaces on air bearings established by the interaction of these aerodynamic features and the air currents.
An essentially laminar air flow is desired since air turbulence (also referred to herein as xe2x80x9cwindagexe2x80x9d) can increase the power consumption of the spindle motor, as well as degrade operational performance of the disc drive. Particularly, nonrepeatable run out (NRRO) error in the placement of the heads adjacent the tracks can be readily induced by windage excitation of the actuator and discs. Such windage excitation arises from large-scale vortices that are shed in the wake of the actuator arms. These vortices are shed at Strouhal""s frequency, which depends on the flow Reynolds number and the actuator geometry.
Such vortices transport the air flow and induce a forcing on the disc, increasing disc flutter (vibration) and power consumption. Further, such vortices, which move at slightly slower speed than the bulk of the mean flow, impinge upon the actuator and modify the mean flow. Vortex shedding frequency changes slightly due to the repeated impingement of the vortices on the actuator. This causes spectral broadening since the shedding frequency itself depends on the incident mean flow. Consequently, a significant amount of energy centered around the Strouhal""s frequency contributes to off-track motion of the actuator.
Prior art efforts to improve laminar flow include disc shrouding, as well as the application of aerodynamically shaping to the actuator arms. Disc shrouding typically involves the placement of a circumferentially extending surface closely adjacent the outermost diameter of the disc pack to reduce windage at the disc boundaries. Aerodynamically shaped actuator arms typically incorporate tapered leading and/or trailing edges which are machined into or separately fabricated and affixed to the edges of the actuator arms. While the foregoing approaches have been operative to improve laminar flow, the continued increases in data aerial recording densities (with track densities of tens of thousands of tracks per radial centimeter) make continued advances highly desirable.
One problem with the aerodynamic shaping of the actuator arms relates to the placement and routing of the conductors used to communicate with the head. The use of magneto-resistive (MR) heads requires multiple conductive paths to facilitate separate write current and read bias current channels for each head. Such conductors can comprise twisted pairs of insulated electrical wire or, more recently, flex circuits comprising one or more semi-flexible dielectric layers which support and insulate electrically conductive traces. The conductors are typically routed along the trailing edges of the respective actuator arms and are supported by bracket flanges which protrude from the actuator arms. The conductors and brackets can thus induce windage effects and reduce the effectiveness of the aerodynamic shaping of the actuator arms.
As aerial recording densities continue to increase, there is a continued need to improve disc drive operational performance by reducing windage effects induced by an actuator, and it is to such improvements that the present invention is directed.
The present invention provides an apparatus for improving disc drive operational performance by reducing windage effects induced by an actuator used to controllably position a head adjacent a disc surface.
In accordance with preferred embodiments, a disc drive is provided with a rotatable actuator which supports one or more read/write heads adjacent a corresponding number of recording surfaces of a rotatable disc pack.
The actuator includes one or more rigid actuator arms that project from an actuator body toward the disc pack. Each actuator arm includes opposing planar top and bottom surfaces and a pair of opposing tapered surfaces which taper to a trailing edge. The top, bottom and tapered surfaces define a cross-sectional enclosure to provide nominally laminar flow of air currents adjacent the actuator arm induced by rotation of the disc pack.
A channel is formed in the enclosure by a plurality of adjoining recessed surfaces to recess a head conductor along the length of the actuator arm within the enclosure to prevent obstruction of the air currents by the conductor. The conductor is preferably a flex circuit with a semi-flexible dielectric layer which supports a plurality of conductive traces.
These and various other features and advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.